With respect to photographic images composed of silver, the ratio of the optical density of the images to the silver content of the images per unit area is generally called the covering power. The covering power is used as a measure for evaluating the optical efficiency of the silver composing the images. The covering power of the silver halide photographic light-sensitive layer generally increases with a decrease in the particle size of silver halide and decreases with an increase in the particle size of silver halide. On the other hand, since the sensitivity of the silver halide emulsion layer generally increases with an increase in the particle size of silver halide, silver halide emulsions having a large particle size are used for producing high speed photographic light-sensitive materials. Accordingly, the high speed photographic light-sensitive materials require a large silver content per unit area in order to obtain a fixed image density. In other words, it is necessary to include a larger amount of silver salt per unit area of the photographic light-sensitive materials in order to obtain both the high sensitivity and the required maximum image density. This is the fact in the conventional high speed photographic light-sensitive materials.
An attempt at improving the covering power while keeping the sensitivity high has been described in British Pat. No. 1,048,057 and No. 1,039,471 and U.S. Pat. No. 3,043,697 and No. 3,446,618, wherein various polymers are added to a high speed coarse silver halide emulsion. All of these techniques are not preferred, because the effect of improving the covering power is not sufficient though there is a some effect. Further, with such techniques, the strength of the coating film deteriorates. Particularly, when a material comprising a coating film having poor strength is processed by an automatic developing apparatus which is conventionally used at present, there is a disadvantage that a part of gelatin in the film dissolves in the developing solution or the fixing solution. The dissolved gelatin will adhere to a conveyor roll of the automatic developing apparatus and be transferred to the light-sensitive material causing contamination of the photographic images.
U.S. Pat. Nos. 2,996,382 and 3,178,282 disclose that photographic images having a high contrast and a high covering power are obtained at a high sensitivity, when a silver halide photographic light-sensitive material in which silver halide coarse particles and silver halide finely-divided particles having fog nuclei in the inside thereof are contained in the same layer or in adjacent layers is used.
However, according to this process, sufficiently high sensitivity and high contrast cannot be obtained. Further, there are faults that a long period of time is required for development when using a conventional low temperature treatment and that a desired effect cannot be obtained with a conventional high temperature rapid treatment.